Note that this is an expansive estimate from an anti-immigration think tank that attempts to count all births to non-citizen mothers who were no longer in the US at some vague point in time afterwards. It does not distinguish between birth tourists attempting to get citizenship for their baby, non-resident mothers who just happened to be here when they gave birth but had no specific intent to get citizenship for their baby, and residents who moved away. And that is an estimate of the total number of birth tourists, so the number who end up claiming more welfare than they pay into the system is going to be some fraction of that.